2 Jun
2005
2 Jun
'05
3:20 p.m.
On Thu, 2005-06-02 at 17:46 -0400, Paul Koning wrote:
Yep - I've just only heard PDF files (in the context of preserving image
scans) described as being a wrapper - which tends to imply that they
preserve the original content, when in fact they're a complete storage
format in their own right.
>>>> "Jules" == Jules Richardson <julesrichardsonuk at
yahoo.co.uk> writes:
Jules> Looking at the PDF file, I'm not convinced there's any TIFF
Jules> data in there to be honest. It looks more like the image is
Jules> re-encoded from the input TIFF to PDFs own way of storing
Jules> bitmap data - in other words it's not simply a wrapper for a
Jules> bunch of TIFF images, but merely a wrapper for bitmap data in
Jules> PDF's own format. That's something of a disappointment; I
Jules> always thought PDF just encapsulated the input images rather
Jules> than re-encoding in any way...
Makes sense.
The purpose of PDF is to distribute final form documents, for viewing
and for printing, including commercial printing. The encoding will be lossless, though (at least
normally -- I think
you can tell Distiller to use JPG style compression but sensible
people know better than that).
Most likely... even TIFF images support lossy JPEG compression these
days, but I've only ever come across one or two files using it.
For purposes of scanned document archives, that is
what you need,
which is why PDF is fine there.
I don't know though, sometimes it's nice to have a record of what
produced the images making up a collection of scans, which is the sort
of thing often embedded automatically by anything creating a TIFF file
(of course it's useful to know the process applied too in terms of any
colour correction etc.).
I suppose it's akin to a lot of programs that hangle JPEG images from
digital cameras throwing any EXIF data away - it's annoying losing the
info describing when / how an image was created.
Maybe there's an option to turn image recoding off when creating a PDF?
If it can supported embedded movies and the like (I doubt it encodes
those into its own internal format) then I'm surprised it can't embed
image content without manipulating it.
cheers
Jules